A workflow processor is an atomic unit of business logic that can modify a query before it is submitted to a search platform, or transform a search response before rendering. This capability is used extensively for doing runtime data cleaning when, for example, it isn’t feasible to re-index a whole collection to fix issues in the source data.
The workflow module ships with a number of query and response processors for common tasks out of the box and it is easy to hook these or your own ones into the query/response lifecycle. These include, but are not restricted to:
Query pattern matching. Intercept queries for common terms that have no corresponding documents in the index (for example, postal codes, phone numbers, or email addresses).
Natural language processing (NLP). Analyse free-text input typed in by the end-user to provide a structured, more specific search command to the backend engine. For example, given the query "restaurants in new york" the NLP pre-processor might produce a structured query along the lines of
category:restaurant and city:nyc. Appkit has integration with a number of third-party NLP parsers, including Expert Systems, WolframAlpha and Smartlogic. More commonly, it is also easy to hook in custom natural language parsers, customised for a particular domain.
Data augmentation. Transform and extend existing data on the fly with re-indexing, for example by fetching external linkages (look up latest stock ticker price, perform relational joins, etc.) or perform translation or lookups (replace ontology terms with common name).
Remove facet filters by pattern. The workflow module includes a comprehensive set of runtime data cleansing tools. When re-indexing is not feasible Appkit can remove irrelevant filters from dynamic navigation options based on for example, regular expression patterns.
The figure below illustrates the query-response lifecycle including a pipeline of workflow processing.
Figure 1. Sample query-response lifecycle involving the workflow engine.
In this example:
A search request is pre-processed before it is translated into an engine-specific command and sent to the search engine (for example, by removing specific forbidden or blacklisted words, applying natural language processing to the free-text portion of the query, etc.).
The data that comes back from the search engine is translated into a generic Appkit search response by the platform adapter, and then fed into a post-processing pipeline (which might, for example, apply regular expressions to remove specific terms from data fields, apply date formatting to facet aggregation values, etc.).
This produces finally a generic Appkit response that is returned to the search application, for rendering or further processing.
Workflow processors: building blocks of data transformation
An Appkit workflow processor is a Java class that is invoked and passed a reference to either a query or response object. A query pre-processor rewrites a query before it is submitted to the underlying search platform. Conversely, a response post-processor transforms a search response (both search results and facets) after it gets returned from a search engine (and before rendering). Workflow processors are typically declared in markup using JSP tags. Multiple processor tags can be specified for sequential processing of queries or responses.
Configuring a workflow pipeline
A workflow pipeline is configured at a platform level. This is useful for example for when you want to reuse processors in several places. This can be done using configuration files, chaining processors together along with a platform as a "workflow platform", which then can be referenced like any other platform.
Lucidworks has packaged up a selection of commonly used response post-processors for reuse.